Temperature change and fire alarm apparatus



Dec. 14, 1954 J. MORRIS, JR 2,697,215

TEMPERATURE CHANGE AND FIRE ALARM APPARATUS Filed Dec. 1, 1951 2 Sheets-Sheet l Inventor 3me: McRms, Tm

A torn e y Dec. 14, 1954 J. MORRIS, JR 2,697,215 TEMPERATURE CHANGE AND FIRE ALARM APPARATUS Filed Dec. 1, 1951 2 Sheets-Sheet 2 lnvem or JE Es Monk's, 75v

y 2% ff A ftorney United States Patent 2,697,215 TEMPERATURE CHANGE AND FIRE ALARM APPARATUS James Morris, Jr., Salford, England Application December 1, 1951, Serial No. 259,345

Claims priority, application Great Britain December 4, 1950 2 Claims. (Cl. 340-427) diiferently heat-absorbent surface finish.

The invention can be used due to friction between the roller and the retarded or Yet again, the propeller shaft of a ship is a sensitive piece of machinery wherein an abnormal heating is indicative of undesirable conditions.

by way of limitation one embodiment of the In the drawings: Figure 1 is a circuit diagram of a fire accordance with the invention;

Fig. 2 is a broken front elevation of a mounting conalarm system in 2,697,215 Patented Dec. 14, 1954 elevation of the appropriate cover used below it;

Figure 9 is a front elevation of part of a Wheatstone bridge where a comparision of temperatures at difierent places is obtained, and

Figure 10 is a similar view of a complementary part at the other place.

arm are arranged in series. The ratio arms 16 and 17 consist of fixed resistors, with a potentiometer adjustment 18 between the series arms 14 and 17. A voltage sensitive indicator 19 is connected across the bridge in well known manner.

The which carries contact or neutral position so long as but wh ch when the bridge mains supply.

Upon closure of contacts 20, 21, a circuit is completed from negative, over contacts 20, 21, through winding 23 of a slow operating relay, over normally-closed contacts will be further described in the Wheatstone bridge in the sense to close contacts 20, 21, being the sense corresponding to a change in the resistances of elements 15 which would result sive heating thereof such as due to fire.

It is desired however that an indication should be given, but of a different kind, should some fault occur from an exces- Y upon a fire or like. The second closure is provided by'the contact set 33 which consists of a moving contact balanced between two fixed contacts. The control of this set is efiected by means of a pair of solenoids 34,, 35,, arranged in opposition on either side thereof and balanced by potentiometer 36. The one solenoid 34 is arranged in series with the bridge and will be affected. by any change in. the current therein; the other solenoid 35 is independent of the bridge. The third closure is that over contacts 38 of relay 39 arranged in series with the indicator 19 across the Wheatstone bridge. These latter two means of closure may be alternative to each other or both may be incorporated in the one system as has been shown.

In describing the operation of this circuit arrangement reference must be made to the respective current and resistance values, but any numerical values that may hereinafter be given are so given solely for the purpose of theoretical explanation and do not necessarily represent the actual values. that would obtain in a system embodying the invention.

The total current through the Wheatstone bridge, i. e. that through the solenoid 34, may be of the order or 50 milli-amperes splitting, when the bridge is balanced, into two parts each of 25 milli-amperes through each of the two parallel branches of the bridge. The resistance of said solenoid 34- is small, say 1 ohm, as compared with that of the bridge as a whole which, with each of the arms at 150 ohms would have an equivalent resistance of 150 ohms. The order of current through the indicator 19 necessary to engage contacts 20 and 21 would be measured in micro-amperes, and would correspond to a change in the relative resistance of arms 13 and 14 of /2 ohm. On the other hand the current to engage contacts 20 and 22, though also in micro-amperes, would correspond to a change (in the opposite sense' of course) of relative resistance at 13, 14 of 2 /2 ohms. In the cases of relay 39 and solenoid 34, the effective currents here would be measured in milliamperes, corresponding in the case of solenoid. 34 to a change of total bridge resistance of say 30 ohms.

With these values in mind the operation of the system becomes clear. Should there occur the untoward condition which has been envisaged as fire, then there will be a small increase in the resistance of one of the elements 15 relative to the other of the pair, an increase of perhaps /2 ohm in say arm 13. This will close contacts 20, 21, so that after the pre-determined delay time the relay 23 operates, giving the fire alarm and locking over contacts 26. Previous to this the movement of pointer 19 over scale 19a will have given visual indication of an undesirable rise in temperature.

Next, suppose that either the arm 13 is onen-circuited or an element in arm 14 is short-circuited, then the contacts 20, 21 will again be closed, but at the same time re ay 39 will o erate and/or contacts 33 will close, in either case causing an immediate operation of relay 28 tin the fault indicator circuit. At this time the relay 23 will not yet have operated, and will now be disabled from so doing by the opening of contacts 3%.

A fault in the nature of a short on arm 13 or in the nature of a break in 14 will engage contacts 20, 22, and/or operate relay 39, and/or close contacts 33.

Finally, a break in the supply across mains leads 11, 12' will close contacts 33 by means of solenoid 35.

If a fire occurs so that the fire alarm operates then if this is followed by the occurrence of a fault it is desirable that the fire-alarm should not be thereby disabled but should continue in operation. To this end the alternative circuit over contacts 40 is provided so that once i the fire-alarm has operated it will be maintained.

The interrela ion between WB, FA and F1 is evident from the above explana tion of operation. Both the fire alarm and the fault indicator systems respond to unbalance of the relative resistance in the legs of the bridge, the direction of operation of indicator 19 depending upon the polarity of the current flowing through the bridge. The fire alarm circuit is initially under the control of the fault indicator circuit so that a current in the bridge of the proper sense to close the fire alarm circuit must be below a certain value to energ1ze the slow acting relay 23. Above that value it will energize relay 39 and close the clrthe three alarm systems cuit of relay 28 and open contacts 30, thus preventing the closing of the circuit of relay 23. Aspointed out relay 28 may also be energized by the closing of contacts 20, 22 and by the closing of contacts 33. However energized, relay 28 operates to disable the fire alarm circuit, provided relay 23 has not become energized and closed its holding circuit before the energization of relay 28.

In Figs. 2, 3, 4, and 5, an arrangement of two sets of three detectors b1 and 01 is shown in which they are mounted under a ceiling 41, and carried by supports 42.

The detectors [)1 may be considered as the more sensitive detectors and the detectors c1 as the less sensitive detectors. The two sets of detectors are enclosed by a cover 43 provided with holes 44 to attord access for the air to the interior and the bottom of the cover has on it imperforate channels 45 to receive the less sensitive detectors c1 and to protect them still further from the heat.

In Figs. 6, 7 and 8 an arrangement is shown wherein detectors b1 and 01 are in separate supports42 below the ceiling 41, either side by side as in Figs. 6 and 8 or end to end as in Fig. 7., the supports 42 having secured to their lower ends a cover 43 having holes 44 below the more sensitive under the less sensitive detectors c1, whereby they are protected.

In Figs. 9 and 10 an arrangement is shown wherein the more sensitive detector b1 is shown in its position and the less sensitive 01 is shown as completely removed from it and is protected, not by a cover as in the previous arrangements described, but by being removed to any desired distance.

his to be understood that the invention is not restricted to the arrangements shown as these are used only for illustration and other arrangements and constructions may be used, modified or altered as requirements demand.

I claim:

1. An electrically operated alarm system comprising an electric circuit including two parallel branches, a

resistance in each branch, the two resistances being differentially responsive to ambient temperature conditions, a bridge connection across the branches including a voltage sensitive indicator having a movable electrical contact and a relay in series with the indicator including a normally open contact, the indicator being operatively responsive to a lesser current than the relay, a fire alarm circuit and a defect alarm circuit each including a normally open contact, a relay solenoid in control of each normally open contact, the solenoid in control of the said contact in the fire alarm circuit being relatively slow operating, and a normally open circuit for each alarm circuit relay solenoid, each normally open circuit including a fixed contact, the two fixed contacts being alternatively engageable by the movable contact of the indicator, the fixed contact in the circuit for the solenoid in control of the contact in the defect alarm circuit being connected in parallel with the normally open contact of the relay in the bridge connection and a normally closed contact in the circuit for the relay solenoid in control of the contact in the fire alarm circuit operatively related to the solenoid in control of the contact in the defect alarm circuit.

2. An electrically operated alarm system as claimed in claim 1 in which the circuit for the relay solenoidin control of the contact in the defect alarm circuit includes another movable contact in parallel with the contact of the relay in the bridge connection, together with a solenoid responsive to current changes in the electric circuit and arranged in control of the said other movable contact.

References Cited in the file of this patent UNIT ED STATES PA ENTS detectors b1 and having noholes. 

